Any discussion of the prior art throughout the specification should in no way be considered as an admission that such prior art is widely known or forms part of the common general knowledge in the field.
In general, the gas flow dynamics for high quality layers deposited by CVD favors laminar flow Laminar flow, as oppose to convective flow, is required to achieve high efficiency of CVD processes and high uniformity of deposited layers.
Referring now to FIG. 1, one type of contemporary reactor is commonly referred to as planetary reactor. The reactor comprises a cylindrical chamber 122 within which chemical vapor deposition is performed, a quartz plate 104 attached to a lid 101 with a gas cooled spacer 120, a centric gas inlet nozzle 107, a rotating susceptor 106 holding a plurality of rotating satellites 127, a heat assembly 126 underneath the susceptor 106, and a gas collect ring 103 surrounding the periphery of the susceptor 106.
Gases enter the cylindrical chamber 122 via the centric inlet nozzle 107 that separates one mixture of gases, such as Group III reactants, from the other, i.e. Group V reactants, prior to their introduction into the cylindrical chamber 122. The centric inlet nozzle 107 and the exhaust 103 are above the susceptor 106. The reactant gases flow in the outwardly radial direction from the centric inlet nozzle 107 to the gas collect ring 103.
As the reactants in carrier gases proceed from the center toward the periphery, a substantial amount of the reactants is consumed along the way due to parasitic reactions forming particles and/or adducts in the gas phase, so as to be called as the depletion effect. As a result, the depositing rate falls along the flow direction. For an outwardly radial flow of reactant gases, the mass density of reactants in the gas phase decreases due to gradually increased cross-section, which forms another inherent source of non-uniform deposition in such a cylindrical chamber.
One contemporary approach to mitigate the depletion effect is to use a high gas flow rate to reduce the concentration gradient along the flow direction, but the drawback of this approach is an inherent decrease in efficiency of CVD processes and an increased consumption of reactant gases. Another contemporary approach to mitigate the depletion effect caused non-uniformity is rotating wafers and/or satellites. Referring to FIG. 1, the susceptor 106 rotates at approximately 10 rpm and the satellites 127 rotate at approximately 50 rpm. Making such kinds of the susceptor capable of rotating multiple wafers and/or satellites in a sealed chamber under very dynamic CVD conditions is inherently expensive and complicated, which has impeded a further increase of the wafer capacity of the planetary reactor.
Furthermore, referring to FIG. 1, due to lack of active gases flowing through, heavy deposits are inherently accumulated on the down surface of the quartz plate 104, which not only depletes the reactants but also deteriorates CVD processing. In order to precisely assembly the components, such as the nozzle 107 and the quartz plate 104 together to the lid 101, the structure of the lid 101 is inherently complex. It is inherently difficult to maintain or clean the lid 101 in routine operation. As a result, repeatability, reproducibility and consistency of the CVD processes can not be ensured. Deformation of the lid 101 under low pressures also influences CVD processing and further impedes the scale up of the cylindrical chamber size in diameter.
Referring to FIG. 2, another type of contemporary reactor is commonly referred to as turbo-disc reactor. The reactor comprises a cylindrical chamber 222, a flow flange 204 where all the reactant gases are distributed and delivered vertically into the cylindrical chamber 222, a wafer carrier 206 spinning at speeds between 500 and 1500 rpm, a heater assembly 226 underneath the wafer carrier 206 configured to heat wafers 200 to desired process temperatures, and an exhaust 203 at the bottom side of the cylindrical chamber 222. The wafer carrier 206 comprises a plurality of pockets, each of which is configured to contain a wafer 200.
In such a reactor, the longitudinal depletion effect of reactants in the flow direction and the effect of lid deposition on CVD processes are substantially mitigated. A few inlets respectively for introduction of reactants require a minimum chamber height for a uniform mixture of reactants above the surface of the wafer carrier 206. An enlarged diameter of a chamber needs an increased height of the cylindrical chamber. Particularly at high pressures and temperatures, thermal convection occurs severely in a large volume of chamber. The gas flow tends to be undesirably turbulent. In order to suppress thermal convection, a high gas flow may be applied and the wafer carrier 206 may spin at very high speeds. One of the drawbacks is an increased consumption of reactants, and the other is that to spin a large wafer carrier at a very high speed substantially without wobbling is inherently extremely difficult. Deformation of the lid 201 under low pressures may influence CVD processing and further impedes the scale up of the cylindrical chamber size in diameter.
Referring to FIG. 3, another type of contemporary reactor is commonly referred to as close coupled showerhead reactor. The reactor comprises a cylindrical chamber 322, a showerhead 304 through where all the reactant gases are distributed and delivered into chamber 322, a wafer carrier 306 rotating at speeds between 5 and 100 rpm, a heater assembly 326 underneath the rotating wafer carrier 306 configured to heat wafers 300 to desired process temperatures, and an exhaust 303 at the bottom side of the cylindrical chamber 322. The wafer carrier 306 comprises a plurality of pockets, each of which is configured to contain a wafer 300.
In such a reactor, thousands of separate fine orifices with complex water passages formed in the showerhead 304 can deliver and distribute gases uniformly over entire wafer carrier 306. The cylindrical chamber height can be substantially reduced to suppress buoyancy as well as parasitic reactions. However, the showerhead 304 is inherently complicated and expensive. Complex water passages around fine orifices face a great risk of leaks. Furthermore, a short distance from the showerhead 304 to the wafer carrier 306 inherently causes heavy deposits on the surface of the showerhead 304. The presence of thousands of separate fine orifices prevents easy and reproducible cleaning after CVD processing. As a result, repeatability, reproducibility and consistency of the CVD processes can not be ensured. Deformation of the lid 301 under low pressures also influences CVD processing and further impedes the scale up of the cylindrical chamber size in diameter.
Referring to FIG. 4, another type of reactor is commonly referred to as rectangular reactor. The reactor may comprise a rectangular chamber 422, the first gas inlet 407 disposed at one side of the cylindrical chamber 422 for a horizontal flow of gases, the second gas inlet 404 located at the top of the cylindrical chamber 422 for a vertical flow of gases, a susceptor 406, a heater 426 beneath the susceptor 406, and an exhaust 403 disposed at the other side of the cylindrical chamber 422.
A horizontal gas stream flows from the first gas inlet 407 to the exhaust 403 parallel to the surface of the susceptor 406. A vertical gas stream flows downwardly to suppress thermal convection for a laminar flow of the horizontal gas stream. Two gas streams mix in the vicinity of the wafers 400, which reduces parasitic reactions in the gas phase. However, the horizontal gas stream still suffers undesired longitudinal depletion effect. The rotation of wafers 400 may be used to compensate the depletion effect. For this type of a non-cylindrical chamber, the side-wall effect on flowing pattern perpendicular to the horizontal gas flow direction can deteriorate uniformity of depositing layers and reduce efficiency of CVD processes, which inherently prevents to build up a large size chamber.
Moreover, throughput requirements from production reactors have become important. The contemporary approach to increase throughput is typically to build larger chambers. Referring to the aforementioned reactors, the top plates of cylindrical chambers are not supported in the center and the gases are introduced through gas inlet devices disposed in the top plate. The thermal and mechanical stress may consequently tend to break top plates prematurely at great costs. So, the aforementioned reactors suffer from inherent deficiencies that tend to detract from their overall utility and desirability.